Manufacture of sulphuric acid by the contact process



F. CARL Filed Jan. 26. 1935 MANUFACTURTURE OF SULPHURIC ACID BY THECONTACT PROCESS March 29, 1938.

Qd/v-T l ATTORNEY.

Patented Mar. Z9, 1938 UNITED STATES PATENT OFFICE MANUFACTURE OFSULPHURIC ACID BY THE CONTACT PROCESS Fred Carl, Wilmington, Del.,assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., acorporation of Delaware Application January 26, 1935, Serial No. 3,565

1 Claim. (Cl. 23-176) This invention relates to an improved process ingeach converter. (See for instance, Bulletin and apparatus for themanufacture of sulphuric 184 of the U. S. Bureau of Mines, compiled byacid by the contact process. More particularly, Wells and Fogg, 1920.)In this system, the sulmy invention deals with the regulation of thephur trioxide gases issuing from the rst con- 5 temperature within theconverter and with the verter, and still containing a considerableamount 5s v cooling of the sulphur trioxide gases issuing from of S02,are passed through a heat exchanger the converter, prior to their entryinto the absorpwhere they are brought in thermal contact with a tiontower, where they are absorbed in dilute relatively cool counter streamof sulphur dioxide sulphuric acid. gases; the cooled gases then proceedinto the l In the specication and claim below, when I second converter,where further conversion of 10 speak of sulphur dioxide gases generally,I am S02 to S03 takes place, and then through a sec# referring to themixture of gases produced in the ond heat exchanger wherein they arelikewise met combustion chamber and containing as principal by a countercurrent of relatively cool sulphur ingredients sulphur dioxide, oxygenand nitrogen. dioxide gases.

l5 When I speak of sulphur trioxide gases, I am re- The heat exchange,however, in this system is 15 ferring to the mixture of gases issuingfrom the incomplete, and it is impractical by this method converter orcontact-chamber, and consisting to cool the final sulphur trioxide gasesbelow principally of sulphur trioxide, nitrogen, excess about 250 C.Consequently, the cooled gases have air, and sometimes unreacted sulphurdioxide. to be passed further through radiators or coolers Thecontact-process of producing sulphuric acid to reduce their temperatureto the desired low de- 20 is well known in the art, and has beendeveloped gree. into a great many systems or modifications. In anothersystem, air is used as the cooling Some of these start with iron pyritesas raw mamedium throughout, but the heat absorbed by it terial. Othersuse brimstone, or crude sulphur. is Wasted.

My present invention is particularly concerned It is accordingly anobject of my invention to 25 with the processes of the latter type.provide a process and apparatus for regulating In all of these systems,the raw material is the temperature of the sulphur trioxide gasesisburned in a combustion chamber, which has at suing from the converter,which is characterized this stage undergone development into a great byboth ilexibility and heat economy.

many modifications.y The combustion gases con- Another object of myinvention is to provide a 30 sisting principally of nitrogen, sulphurdioxide System Wheren the apparatus fOr C001ng 0f the and oxygen arethen cooled to an optimum tem- S03 gases from the converter cooperateswith the perature for conversion into sulphur trioxide, apparatus forcooling the SO2 gases from the' Comusually around 325 to 425 C., and arepassed on bustion chamber, to produce amaximum economy into a converter,or contact chamber, where they and conservation of the heat stored inboth. 35 come vin contact with catalytic mass, usually A still furtherobject is to provide a system posplatinum suitably supported on acarrier. 'I'he sessing means for ready and easy control of the catalystpromotes the reaction between the SO2 temperature Within the converterand of the final and oxygen within the incoming mixture, and temperature0f the Sulphur trioxide gaSeS- 40 produces S03. Considerable heat isdeveloped A still further object of my invention is to pro- 40 duringthis stage which must be conducted away vide a system wherein the excessheat in the refor best practical effects, since at higher temperaactiongases is: converted into useful steam energy. tures the S03 tends todecompose back into S02 Other and further important objects of thisinand oxygen. The sulphur trioxide gases issuing vention will appear asthe description proceeds. 45

from the converter must be cooled for the further The means by Whichthis Combination 0f desirreason that their absorption in sulphuric acidis ableI ends is accomplished will be best understood more efficient atlower temperatures than at a by reference to the annexed drawing whichis higher one. hereby made a part of this description. In this Manysystems have been developed in the art drawing, the flgllre representsdiagrammateally for accomplishing each stage of the above cona :flowsheet of apparatus by which my process is tinuous process in general,and the last stage in carried out, the arrows indicating the directionparticular. of ow.

In a system known as Badische, two converters In this figure, I is acombustion chamber operare used in series, with avheat exchangeriollowating under superatmospheric pressure and sup- 55 plied withpowdered or molten sulphur under pressure through valved line I I, andwith hot, dry air through valved line I0. 'I'he valves on these linespermit a regulation of both the amount and proportions of these rawmaterials. 2 is a firetube boiler, though other types of steamgenerators used vwithout departing from .the spirit of my invention.This boiler is equipped` with the usual auxiliaries of a. steam boiler(not shown). chamber flow through the re-tubes in this boiler',

and the ow is so proportioned thatlinderl'f ull;A operation of the plantit will deliver a'igaswhse temperature is lower than the optimum.required-v for the gases entering the first*converter:1A 3 slall..converter containing a catalytically active massel and 4 is a heatexchanger. 5 isanotherconverter and 6 is a nal heat exchanger'f'Additional* stages of converter and heat exchangermay be ff installed ifdesired. The flow lines Will'b'e described 'in connection Withfadescription of the l operation.

To operate my process, moltensulphur and hot,

dry air are supplied to the combustion 'chamber- I v'in regulable amountand combine to form a. mix-'- ture of sulphur dioxide, oxygen andfnitrogen, which passes intothe boiler setting 2 vat highft'emperature.In general I prefer tov regulate thecormv bustion so that this gascontains 8 to 10%` sulphur dioxide, byvolume, though -this'composition-may.

be" greatlyifvaried Vwithout 'departing from the'. spirit-of myinvention. In the'boiler-setting 2 'the gas is cooled to about 250 C.,thesteam generated therebyvbeing passed into the plant mainsor used forany vother. useful-purpose such, for examples, as driving thevariousipumpsfblowers, etc., ,used around the sulphuric acid plant. Byvmeans ofthe valved by-pa'ss line lzfthrough'which hot gas from thecombustion chamber ispassed, .the-temaA perature ofthe gas leaving theboileris brought up to a temperature suitable for catalytic con'-vversion, say about 325;to'425. C., andispassed into 'converter'. 3. Inthis converter, 'thefgreater. portion of the SO2 in the mixture isconverted .to S03, V(from "about 60%' `to` aboutr 80%), and

thegas temperature rises'(usuallyby-about 1501 to Y 1n `which thesulphur 1s liquefied locally just prior The hot gas leaving-thisconverter ispassed'tow heat exchanger 4 where its temperature'is againreduced to a point suitable for entering the-second converter 5;" thecoolingwmediumbeing the air:

subsequently used in the-combustion chamber. After passagethroughconverter 5, where another temperature risel occurs, much'milder'thaninther first converter, rtheV gas passes `to the-finalheatV exchanger: 6,where itgives up most of its excess heat to the air suppliedtothe:system. The exit gasfrom thisexchanger, nowcontaining nearly f allof its sulphur `in the form of S03; is passed-to a conventionalabsorption system. l.

Through 4pipef'l dry airi'atessentiallyatmos'- phericV temperatureyis-supplied to the system.

under pressure. i YBy means -ofV thevalved-by-pass 8, enoughof this'airis'passed into line 9 to mainf tain the proper temperature in the gasrentering converter-*5. The'control here is simple and easy.

'I'he moreair is passed through lthis line, `the lower will .be thetemperature` of the gas entering con 'I'he Ybalance of the air from pipe.1, ywhich constitutes its greater part, passes through verterV 5.

exchanger 6, cools ,the sulphur-trioxide-laden gas from' the convertersystem, Yand is thereby raised in temperature. temperature isregulatedeas just describedyen'- teringexchanger-4 is-furtherheatedtherein and The hot gases from the combustion "the"'combustionchamber, the increase being of theY .orderffof 14009176: vhigher.onlyifacilitates the burning of the sulphur, but

The .partly heated air, Whose cools the gas leaving converter 3 prior toits entry into converter 5. This heated air leaving exchanger 4 is thenconducted into the combustion chamber through pipe I0, and used in theburning of the sulphur in said combustion chamber. It contains a largerpart of the heat evolved upon the conversion of the SO2 to S03, and addsthis heat to thatagenerated in the combustion chamber when the sulphurburns to SO2. Thisk results in` an appreciably higher flame temperaturein 'I'his increase not it permitsmore efficient recovery of this heatin4the'form"of'steam1when this superheated gas ispassed into'. .theboiler. It will be obvious that all'par'ts of the'system, including theconnecting Jpipesgishouldtorfbesteconomy be well insulated against .theloss of heat.

By this method of operating, a large part of the heat Agenerated in rthesystem, not'only from :the

combustion of the sulphur, :but alsofrom-the 'subVV sequent oxidationofthe sulphury dioxide, is're-Y coveredin the form of -highnpressuresteam, and` the gas ycontaining' sulphur trioxideis delivered totheabsorption'system'at a suflcientlylow tem- .Y

perature, say aboutl 50," C., so that no furthercooling. thereof isnecessary. Moreover, by arrangingr the apparatus as shown, whereby theairtravels successively-:through the various heat exchangers, incounter-current relation to thev converter gases,.and by-the provisionof 4suitable by-passesm for t-he air, -theftemperature regulationV atevery point in ithe system becomesgreatly facilitated,

and the efficiency of heat-recovery may be brought to a maximum.Finally, the apparatus by which this is accomplished is lessV costly andmore com-- u pact than-the apparatus formerly used, in which the heat ofreaction was dissipated to the airor' to coolingwater which ran -to thesewer.`

of operation-and apparatus -employed may be varied and modifiedWithinvwiderlimits, Without departingfrom the spiritof this invention.Thus, Y

in lieu of. a liquid sulphur burner, apowdered sulphur burner maybeused,...or one of those types tocombustion.. Instead of a fire-tubeboiler, any.4

suitable typeof steam generator maybe applied.

Its tubes may be made ofthe usual materials forv steam boilers, forinstance, steel, since at the high temperatureoftheSOz gases nocondensation of f (See l acid andsubsequent corrosion takeY place.further U. S. Patent No. 1,545,381). v

InsteadY of two converter-heat-exchanger stages.

in series, any number of Vstages may be installed.

The lefliciencycf. conversion-generally increases 'Y withthe` number ofstages, but so vdoes also the cost of the installation.

A packlter may be interposed,` if desired, be-` tween the. sulphurdioxide cooler (i. e. the steam generator) and the first converter; Whendry vconditioned airis used, this will generally be unnecessary.` Butwhere conditioned air is unavailableV or impractical, lthe filter will;by removing Ydust particles and impurities, prolong the active life ofthe catalytic mass inside the converters.

The heat exchangers may be ofthe conventional design, or of any optionalspecial design. It is Y understood, of course, thatv the counter currentgases in the heat exchangers flow in separate channelswithout physicalcontact, butthe walls of the tubesv of Yiiow are'madelof heat conduct:`

. 40 l It willbe understood that my preferred system i for cooling-airto said second heat exchanger, an

unobstructed conduit for cooling-air between said second heat exchangerand said first heat exchanger, a by-pass conduit for cooling-airextending from said inlet air conduit around said second heat exchangerto the air conduit between said heat exchangers, a valve in saidby-pass, an unobstructed air conduit extending from said first heatexchanger to the combustion space of said furnace, the conduitsotherwise providing an unbranching passage for the air through the heatexchangers, in which it is in indirect heat exchange with the oxidizedsulphur gases, to the combustion space .of the furnace.

FRED CARL.

